{% comment %} Self contained warning block that should appear if a form field was not rendered on the page. It contains some JavaScript which checks again if a fields was really not rendered. This is necessary to avoid false positives when the user includes the field with handwritten HTML. We hide all warnings at page load. The reason is that we might remove the warning when we think it's not valid. And that might result in a flash of the message, then disappearing again. {% endcomment %}